1. Field of the Invention
The present invention relates to an image processing apparatus for electrically processing image information.
2. Description of the Prior Art
When an original image is photoelectrically read and an image is recorded based on the read image signal, the image may be optically enlarged or reduced or a recording pixel density may be changed in recording the image. However, such methods are not advisable because they lead to an increase of the size and complexity of apparatus.
In the past, a digital image data handling apparatus did not need gray level processing. However, as the application field expands from a facsimile apparatus to a copying machine, demand for high quality of image increases and gray level processing is required to reproduce half-tone image such as a photograph.
In most gray level processing methods, a plurality of black and white dot images are blocked as is done in a dither method, and the gray level is reproduced in accordance with the number of black or white dot images in the block.
A variable magnification processing has been proposed, in which an image is enlarged or reduced by adding or taking out (interlacing) digital image data.
However, when the gray level processing is combined with the variable magnification processing, image quality may be degraded, as will be explained below. When the image data is gray-level processed by the dither method and the processed data is then magnified, a size of a predetermined size of pixel unit (pixel matrix) for reproducing the gray level changes and hence white/black areas per unit area change. As a result, a required tonality is not attained and the image is not reproduced with a correct density. That is, if the magnification processing is effected after the dither processing, the dither-processed pattern is destroyed and the reproducibility by the dither matrix is lost. In order to prevent this, the dither pattern may be changed or the dither output may be varied in accordance with magnification but this is not advisable because it complicates the circuit configuration and increases the size of the apparatus.